Salmon farming begins in freshwater. Farmers strip ready-to spawn broodstock salmon of eggs and sperm. Prior to fertilization, the eggs are referred to as "green eggs". Once fertilized, the eggs are stored in trays, boxes or baskets fitted with mesh and are constantly flushed with water as they develop. The advanced fertilized eggs when developed to the point where the eyes of the embryo are apparent are referred to as "eyed eggs". The time from fertilization to hatching takes roughly 40 days, at 10.degree. C. although the process varies with each species and is particularly sensitive to water temperature. When the eggs hatch, the resulting fry are referred to as alevin or sac fry. In this stage, the sac fry are still attached to, and obtain nourishment from, the yolk sac. The sac fry tend to hug the bottom of the container in which they are kept.
After the nutrients in the yolk sac are depleted, the fry swim to the surface and begin feeding. At this point, the fry are referred to as "starter fed" or "swim up" fry. When the fry, or fingerlings, reach the feeding stage, they are moved to troughs, or tanks.
Rearing fry to the next, smolt stage, at which time the fish are capable of adapting to a marine environment, takes from zero to 15 months depending on the species. Smoltification changes a fish's body shape and physical coloration. Once salmon reach this stage, the two-to-three-ounce fish are released into the ocean or transported to saltwater netpens anchored close to shore to begin the grow-out phase.
During the grow-out phase, the salmon are given a commercial diet for from nine months (for coho) to two years (for Atlantic salmon). The fish are typically fed 2 percent of their body weight per day; between one and a half and two pounds of feed produce one pound of salmon. It is common for fertilized fish eggs to be harvested at one location, transported to a second location, and hatched at that location.
At the eyed stage the salmonid embryo can be transported over long distances. During transportation and incubation, nevertheless the eggs of most aquatic creatures must be kept within a given temperature range. For example, the eyed eggs of salmonids should be kept between 35.degree. and 45.degree. Fahrenheit while the eggs are being transported. Heretofore, separate pieces of equipment have been employed to transport and incubate the fertilized eggs and then grow out the fry. One heretofore proposed transport device is disclosed in U.S. Pat. No. 3,194,211 issued Jul. 13, 1965 to Stanek for TRANSPORT AND COOLING CONTAINER FOR LIVING FISH ROE AND/OR FRY; and other transport containers are discussed in that patent. U.S. Pat. No. 3,024,764 issued Mar. 13, 1962 to Brittain et al for FISH EGGS INCUBATORS; U.S. Pat. No. 4,014,293 issued Mar. 29, 1977 to Salter for FISH EGG INCUBATOR; U.S. Pat. No. 4,094,270 issued Jun. 13, 1978 to WHITLOCK for FISH EGG INCUBATORS; U.S. Pat. No. 4,180,012 issued Dec. 25, 1979 to Zenger, Sr. for FISH EGG INCUBATOR WITH FRY RELEASE MEANS; and U.S. Pat. No. 4,182,269 issued Jan. 8, 1980 to Young, II for INCUBATOR FOR SALMON ID EGGS AND ALEVIN disclose heretofore proposed incubators.
Also, it is often desirable to plant fish in spawning streams to supplement natural spawning runs. Currently, in planting fish in spawning streams, eggs are also fertilized at one location, transported in an appropriate container to the stream, and placed in a separate incubator at the stream where they are hatched. After the fry reach the feeding stage, they are released into the stream.
This need for two separate pieces of equipment, one for transporting and another for incubating eggs and then growing out the fry hatched therefrom increases significantly the cost of raising fish to the fry or fingerling stage. Also, heretofore proposed fish egg transporting devices and incubators tend to have such disadvantages as complexity, high cost, low structural integrety and survival rates as well as the quality of the fry are often marginal.
Currently, transportation of fish fry is accomplished by placing the fry in water in a closed container. Air is left in the closed container to allow oxygenation of the fish during transportation. The fry are then transported to another location. The problem with this method is that the number of fish that may be transported per container is undesirably limited because the closed container can be filled to only one-third of its capacity with water.